The present invention relates to solid state lasers having an output in the near infrared, especially those lasers which have a compact size and have a high peak output power.
Recent advances in lasers have lead to monoblock lasers which feature a number of optical elements assembled on a substrate to provide a single piece laser of a compact size. These monoblock lasers are used in the area of range finding and surveying applications, and have been used in commercial and military applications. For example, U.S. Pat. Nos. 6,556,614, 6,373,865 and 6,744,801 to Nettleton show monolithic and pseudo-monblithic laser resonators on a substrate.
Monoblock lasers resonators have a set of gain rods, generally a Q-switch and an OPO with various mirrors arranged linearly along the length of a substrate. Light from flash lamps or from diode lasers is coupled into a rod of lasing material such as Nd:YAG or the like, and the light moves bidirectionally through the rod, bouncing between a highly reflective (HR) mirror and an output coupler (OC) mirror placed on either end of the lasing rod. In range finding applications there generally is a Q-switch to provide a pulsed output.
In some applications, an eye-safe (near infrared wavelength (e.g., 1.54 micron)) laser output is desirable. To that end, an optical parametric oscillator (OPO) is introduced into the optical path, to change the output wavelength from 1.1 micron, the output wavelength of the commonly used Nd:YAG lasing material, to a desired eye-safe wavelength such as 1.54 micron.
Certain monoblock laser designs have combinations of lamps above the gain rods and/or discrete reflectors placed underneath the substrate, in order to achieve acceptable lasing thresholds at a given power consumption. This method suffers from undesirably high scattering losses in the fine-ground substrate as well as angle-of-acceptance issues which prevent the reflected light from entering the gain rods. Another known method includes gluing a metal strip under the gain rods, which compromises glue joint integrity and leads to peeling of the metal strip because of undesirable thermal expansion coefficient mismatches. Furthermore, as monoblock lasers with wavelength shifting are commonly used in applications where power consumption must be minimized, it is desirable to minimize the amount of power required to operate the laser.
Consequently, a need exists for a monoblock laser which couples light into the gain rods more efficiently, but which does not increase overall input power requirements for the laser.